Rheostat



' '(No Model.)

A. J. SHAW.

RHEOSTAT.

No. 468,'752" Patented Feb. 9, 1892.

AL TON J. sHAm UNITED STATES PATENT OFFICE.

ALTON J. SHAW, OF MU'SKEGON, 'MICHIGAN RH EOSTAT.

SPECIFICATION forming part of Letters Patent No. 468,'752, dated February 9, 1892. Application filed October 15, 1891, Serial No. 408.794. No model.)

To all whom it may conccrm Be it known that I, ALTON J. SHAW, a citizen of'the United States, residing at Muskegon, n the county of Muskegon and State of Michigan, have invented certain new and useful Improvements in Eheostats, of which the following is a specification.

My invention relates to rheostats or artifical resistances for employment in connection wth electrical apparatus; and it consists in a novel Construction of the same, hereinafter fully set forth, by which I am enabled to obtain any required degreeof resistance and to vary the same quickly, uniformly,'and With certainty without the liability of dangerous heating, burning out, or sparking;

Figure 1 is a perspective view of a rheostat embodying ny improvements; Fig. 2, a side elevation partly in section; Fig. 3, an enlarged sectional View illustrating the construction of the snap-switchg'Fig. 4, an end view of the same, and Fig. 5 a cross-section on the line :c a: of-Fig. 2. v

Briefly stated the rheostat consists of a solid or integral bar, either straight or curved, and preferably of carbon, a m'iXture of carbon and clay or other inferior conductor suited to the particular use in'view, and a series of transverse plates embedded in and constitutingan integral part of the complete bar, but 'projecting` above the main body thereof sufficiently to form contact points or surfaces for the brushes, springs', or other contact devices to bear upon. Prior to my invention rheostats have been made in a variety of forms;

and carbon, clay, steatite, and various other materials, as well as compositions of dilterent materials, have been employed to give the desired resistance. So, too, plates of metal or alloy, either of one or two Varieties, have been bound together or held'in permanent contact, so as to constitute in cifect one continuous bar, certain plates of the series being arranged to project and form the contact-surfaces. In the use of carbon, clay, and compositions of these and analogous substances a difficulty has been encountered which I aim to overcome by my invention, and that is the heating of the Contacts when such have consisted of sliding fingers, rin'gs, or springs moving along one side of the bar. lVith such prior constructions, if the current passed is heavy, bars of consider-able cross-section must y be used, and as they must have a high spe cificresistance current `entering at the side of the bar will not distribute itself throughout its entire area or mass, but will tend to pass along one side of the bar. Dhe seemingly obvons renedy for this difficulty is to v make the bar of a lower specific resistance transversely than longitudinally; but if the bar be made homogeneous this cannot be done; but by my Construction this desirable result can be attainedwith ease and certainty. By embedding in the bar plates of metal, pure carbon, or other substanee having a lower specific resistance than the body of. the bar itself I insure the distribution of the current throughout the area of said plate, and consequently throughout the body of material intervening between each plate and the next, and thus overcome at once the two difficulties above indicated-viz., the heating and the unequal distribution of the current throughout the mass of the bar.

Referri ng again to the drawings, A indicates the resisting bar or body of the rheostat, which I preferto make in one homogeneous mass, and B'plates of metal, pure carbon, or other suitable material embedded in and constituting an integral part of' the complete bar. The bar may be of any desired formin cross-section, and the plates' are ordinarily conformed more or less closely to the section` of the bar, though I pretor that the lower and sideedges of the plates be surrounded by or' inclosed in the body of the bar A, as best shown. in Fig.-5.^

In practice I find a composition of earbon and clay admirably suited to the purpose stated, the specific resistance varying as the' proportions of carbon and clay are v`aried,increasing and decreasing in direct consonance with the decrease or increase in 'the relative proportion of clay used. V As the requirenents of the art call for 'a very wide range and as the properproportions for diltereut uses are already well understood, I do not mean to restrict myself to anydefinite proportions whatever, nor, in fact, to the use ot' these particular materials, but propose to use any material or composipresent.

durable.

tion of materials nowknown as suitable to the purpose, but may say 'that for ordinary purposes equal parts of carbon and clay may be advantageouslyused. These materials are moistened and worked together with water or with any suitable liquidor binding agent and preferably pressed into shape in a mold containing the plates B, suitably spaced; but obviously the plates may be inserted into the bar after itjhas assumed its form, but before it 'has become solidified. The bar may be dried With or without pressure or may be baked, or, as I prefer, it may be first firmly compressed and then baked to renderitnore If desired, the mixture may be treated in any well-known nanner to eliminate or to render ;practically incombustible any combustible elements that may be Pure carbon in the free stateas, tor in- -stance, in the form of graphite-is infnsible. various compounds of carbon and other substances are combustible; but by first washing with sulphuric acid, gas-coke, graphite, or other forms of carbon containing more or less of impurities and subsequently removing all trace of acid by thorough washing in water I am enabled to obtain a grade of carbon well suited to the purposes of this invention. Such treatnent'is. not claimed by me; nor is it deemed necessary ordinarily. By mixing ordinary gas-retort oarbon in the form of pow der with clay a very satisfactory composition is obtained; v i

As shown in Figs. 1, 2, and 3, the plates B have their upper ends bent laterally, so as to afford a broad flat bearing-face for the contact fin gers, springs, plates, toes, or brushes, as the case maybe, which are indicatedin the drawings by the' letter C. In practice I prefer a series of gravitating toes hung upon a eral name of "snap switchesf common rod or pivot, as shown in Figs. 1 and 2, the' pivot-red being carried by a sliding block or head D, which may be guided upon rods or in any other convenient Inanner, the block or the rods, one or the other, being duly insulated. It is desirable in this class of devices thatwhen the contact toes, brushes, or springs leave the last plate or contact 'of the series the break shall be quickly made and of such width as to prevent sparking. Various devices to this end have been 'devised, and' these' are known u'nd'er'the gen- Such a device is provided in my rheostat andis formed by hinging the last plate F ot' the series and holding it normallyin its upright position by means of a spring, weight, or other device, a 'spring being preferred because of its ouicker action.

The construction referred to is illustrated in Figs. 2 and 3, inwhich the last plate but one of the series is represented as attached to or provided with a supplemental plate B',

having a lug or extension b, which projects through the 'end of the bar and forms a bear.-

ing for the last plate F of the series. supplemental plate B' is formed with ears c, between which the lower end of the last plate is hinged or pivoted, as'shown,in Figs. 1, 2, 3, and 4, a spring hearing against the outside face of the plate F and serving to hold it normally in' an upright position andin contact with the lug b.

In Fig. 2 I have represented a spring Il in spiral form encirclinga rod or stem, the inner end of which screws into the bar A or into the plate B while its head or outer end forms a bearing for one -end of the spring.

In Fig. 3 I have shown a flat spring H', the

lower end of which is Secured to the lower end of plate B'; but it is apparent that the The precise arrangement of the spring is immai perfeotdistribution of the current 'over the entire sectional area of the bar than is otherwise practicable;

The form, size, and number ot' the openngs ot' the plates are im material and may be varied, as desired. Bin'ding-posts, olamps, or other convenient means of connection for the linewires will be provided for the first plate Bof the series and for the contact .toes, springs, or plates C.

The bar A may be Secured upon a piece of wood or other suitable material or otherwise held in place, and, as above mentioned, may be either straight or curved, and the curvature may be in any direction desired.

The plates B are preferably made of iron and will in practice be struck un or stamped from sheet metal.

lt is desirable to employ in connection with the bar A of carbon or other composition transverse plates of some material having the same or substantially the same relative expansion and contraction under changes of temperature,'in order that the contact may be preserved and kept un-lforn, and in ordeg further, that the bar may not bc broken or destroyed by more rapid expansion of the plates than of the bar. `For this' reason it may in some cases bedesirable to use pure carbon plates instead of metallic plates; butbycareful selection from well-known metals and conpositions it is entirely feasible to make such combinations as shall avoid any difficulty which might possibly arise through injudicious combinations.

.As the rates of expansion and, contraction ot' almost all known substances have been determined and tabulated 'and as`I do not in any manner restrict myself to any particular IOC IIO

combinatio'n of substances or materials it is deemed unnecessary to specify any particular combinaton. I

Having thus described my invention, what I claim is- 1. In a rheostat, an integral bar or body con stituting the resistance and a series of plates embedded in said bar at points between its ends and projecting therefrom at one side to form contact-surfaces, the plate's being of -lower specific resistance than the body of the bar. e

2. Aniutegral resistance bar, block, or body consisting of a main body of oomparatively low conducting-power and a series of transve-se plates embedded in said body at interv Vals throughout its length, said plates having a lower specific electrical resistance than the material conposing the main body.

3. Phe herein-described resistan ce bar or block, consisting of a body A of material of comparatively high specific resitance and a series .of transverse plates B of material havplates B, the platesbeiug formed with one or more openings from face to face and the substance of the bar passing through and filling said opening, substantially -as shown and described.

5. In conbination with bar -A, provided with plates B, end plate F, hinged to Swing away from the end of the bar, a spring bearing against 'said plate and servingto hold the same normally against the end of the bar, and a movable contact arranged to ride over the plate B in succession and. to move the plate F away from the end of the bar and finally to pass out of contact with said plate and permit its quicker return to its normal position. G. In combination with bar A and plates B,- novable contact C, hinged plate F, and spring H,`serving to hold the plate F normally in an 'upright position.

7. In combinationwith bar A, provided with plates B, plate B', provided with lug a and ears b,plate F, hinged in said cars; spring H, and movable contact C.

In witness whereof I hereunto set my hand in the presence of two witnesses.

ALTON J. SHAW. Witnesses- C. J. -SAWYER, CHAS. L. GRIFFIN. 

